TL;DR: A spot voyage's result comes down to a few speed and timing calls. The inputs behind them keep changing after departure, and most plans leave the operator to reconcile them by hand. Plans that hold weigh them as one objective and recalculate as the voyage goes on. To check, replay a finished voyage using only what was known on departure day.
Where a spot voyage's result is decided
For a tanker trading spot, the fixture sets the freight rate. What the voyage earns depends on how much of that rate is left at the end:
- the fuel burned
- the days taken
- whether the ship arrives when arriving is worth something
That is the gap between the rate and the time charter equivalent (TCE), the daily earnings figure most owners use to judge a voyage.
Those outcomes come down to a handful of speed and timing decisions. They are often made under pressure, and often on a plan that was fixed on the day the ship left port. ZeroNorth has replayed hundreds of finished voyages to see where those decisions hold up and where they don't. The patterns in this article come from that work.
Operators know plans drift, and most have learned to live with it. What rarely gets measured is what that drift costs: the gap between the voyage estimate and the final result.
How a voyage plan is usually built
Most voyage plans start with an ETA. It is set by the laycan, or by a market the owner wants to reach. The route is then optimised against the weather forecast up to that ETA. The master receives speed instructions in segments, each kept as long as practical, so the ship isn't being re-instructed every few hours.
On departure day, that is a sound plan. The trouble is that almost everything it was built on starts to move once the ship is under way.
Four things that change after departure
Market rate: time can be worth more than fuel
Freight rates move through the day, and the market the ETA was aimed at can firm or soften mid-voyage. If forward rates point to a strong market ahead, getting there sooner can pay for itself, because the time saved is worth more than the extra bunkers. If the market cools, the answer flips, and a slower, cheaper arrival may protect more of the margin.
Bunker cost: every extra knot has to earn its place
Fuel is the other side of that trade-off. While bunkers stay expensive, speed has to justify itself. The balance between the value of time and the cost of fuel isn't settled once at the start. It has to be recalculated throughout the voyage as both move.
Port terms: arriving early can be worth nothing
The laycan, notice of readiness terms and demurrage rates decide whether an early arrival is worth anything. Pushing for a hot market only pays off if the ship can start earning when it gets there. As Bjørn Ørving, VP Growth Strategy at ZeroNorth, puts it: "Yes, the market is hot, so full throttle. But if you land there at Christmas, it's worth nothing."
Weather: the forecast ends before the voyage does
A detailed forecast covers roughly the next seven days. Beyond that, a plan has to rely on seasonal patterns, and averages can hide how volatile a region really is: an area that looks calm on average can still turn dangerous quickly. A good plan considers seasonal risk, not only seasonal averages, and keeps a sensible distance from the worst of it.
Why a speed and consumption table isn't enough
The traditional way to plan speed through weather is a speed and consumption table: at Beaufort 4 and sea state 3, the ship burns a given amount of fuel at a given speed. That is a simplification. Wind, swell, waves and current each push on the vessel from a particular direction, and that push can work for the ship or against it.
A weather routing plan that places the ship well in the weather can pick up favourable conditions, or at least reduce what is working against it. Getting that right depends on how this particular vessel responds to this particular combination of conditions. It matters even at full speed: a ship pushing hard for a strong market still gains from where it sits in the weather.
Where value leaks: four decisions made separately
Each of these calls is usually made well, by experienced people. The gap is that they are made apart.
- Separate conversations: the weather and the ETA in one place, the market and the throttle in another, port terms somewhere else.
- Competing objectives: move as fast as possible, don't arrive before the laycan opens, and watch the fuel because bunkers are expensive.
- Reconciled by hand: the operator ends up getting everyone aligned on one objective, when the plan itself could be doing that work.
- The result: each call makes sense on its own, but together they leak value.
An example (illustrative, not a real voyage): a laden tanker leaves port on a plan built for a firm market. Midway, forward rates rise and the ship is sent to full speed. The weather routing is updated for the new speed, but nobody rechecks the discharge port's laycan. The ship arrives early, waits at anchor, and the extra fuel buys nothing.
Plan A vs Plan B: the same voyage, planned two ways
The difference between a plan that drifts and one that holds comes down to how each input is handled after departure.
What a plan that keeps up looks like
The answer isn't a cleverer departure-day plan. It is a plan that keeps working after the ship leaves port.
- One objective: the market rate, bunker cost, port terms and weather are weighed together, not in separate calls.
- Recalculated as things change: sometimes arriving sooner is worth the extra fuel, and sometimes slowing down protects the margin. The plan should tell the difference on day ten as well as on day one.
- Refreshed regularly: on live voyages, ZeroNorth re-optimises throughout, typically adjusting the plan every second day to the newest forecast.
- People stay in charge: the operator and the master still make the calls. The plan does the reconciling, so the decision in front of them reflects what is happening now.
How to test your own plans: replay a voyage to see the difference
The fairest way to judge any voyage plan, including ours, is a backtest. A backtest replays a finished voyage from its departure day and compares the result with how the voyage was actually sailed. It takes four steps.
Why the replay only uses what you knew on the day
The "same information" rule is what gives the result meaning. A replay that used data the operator didn't have on departure day would prove nothing. Using only the forecast, rates and prices from that day means the comparison is between two decisions made with the same knowledge.
When a replay comes back negative
Not every replay comes out ahead. In one North Atlantic crossing from the UK to the US, the replayed plan took a noticeably more southerly route than the ship actually sailed. On paper, it cost money. But the actual vessel, on its more direct route, went through Beaufort 6 to 7. The replay hadn't predicted that storm. It had allowed for the risk of one, and chosen the route that kept clear of it.
That is a trade-off worth making. As Bjørn Ørving put it:
“I would rather lose $5,000 nine times than end up in one situation where it's a question of whether this vessel gets through.”
Beyond the cost, there are the people on board. Shipping is conservative for good reasons, and a voyage plan should be too. That is why we show the negative replays alongside the rest.
Questions to ask your team
- When did we last recheck speed against the market mid-voyage, and what triggered it?
- Who owns the trade-off between time and fuel on a live voyage: chartering, operations or the master?
- How do the laycan, notice of readiness and demurrage terms feed into the speed instruction, if at all?
- Is our weather routing based on a speed and consumption table, or on how this vessel behaves in this wind, swell and current?
- Do our operators question the route they are given, or follow it as instructed?
- Have we ever replayed a finished voyage calmly, away from the pressure of the day? It is a useful exercise with any provider, including your current one.
See it on one of your own voyages
Send us a few recent voyages. We'll replay them using only what you knew on departure day, then walk you through the method and the results, including any that come back negative.
